1. Field of the Invention
The present invention relates generally to the art of folding and packaging sheets of pliable material, such as plastic or paper. The sheets may be multi-layer sheets, such as plastic bags. More specifically, the present invention relates to the art of accurately folding sheet material at a high rate of speed in a machine which may be readily modified to produce different types and sizes of products.
2. Description of the Prior Art
A number of different types of machines are known in the art for folding sheets of pliable material. Such sheet material includes paper sheets, such as tissue, and plastic sheets, such as bags. While a variety of such folded products are known, the prior art will be described, for purposes of illustration, by reference to the folding of plastic bags, such as trash bags, kitchen garbage bags, food storage bags, etc.
In the preparation of such products, plastic film tubing is typically sealed and perforated in a bag machine to produce connected bags. The bags are then separated from one another by tearing apart the perforations. In the commercially available folders known to the present inventor, the individual bags are then conveyed in a "lay flat" condition onto a table where the folding operations commence. In such known folders, the sheet is creased at a preselected location to form a fold as the sheet is pushed through an upper table onto a table below. Subsequent folding operations occur until a desired number of folds have been formed.
Several problems are encountered with such prior art folding machines. First, it has been difficult to correctly time the folding with the upstream operations, resulting in waste or poor quality product. Second, such machines are not quickly modified for different numbers of folds or different size products. Third, because speed is important in any folding and packaging operation, control of the orientation of the sheet material in such prior art machines has been a substantial problem. Such sheets may, at line speeds of over 150 feet per minute, have a tendency to become airborn as they move from bag machine to folding table. When this happens, the product can become improperly oriented, so that the folds will not be square to the edges of the product. Fourth, if the above problems are encountered and the folds are not square, the resulting product will be of poor quality. For example, the product will be larger than would be the case if all the folds were square. This problem is easily spotted upon examination of many commercial products found on store shelves at the present time. Moreover, if products are produced which are larger than desired, provision must be made to accommodate the larger products in the packaging. In the prior art, this has been accomplished by providing boxes which are larger than those which would be necessary for precisely folded products. Larger boxes add packaging material cost and additional expense in the transportation and display of the bag products.
A folding and packaging system which overcomes the aforementioned disadvantages of the prior art would represent a significant advance in the art.